THE COILED-COIL REGION OF THE G-PROTEIN BETA-SUBUNIT - MUTATIONAL ANALYSIS OF G-GAMMA AND EFFECTOR INTERACTIONS

The beta and gamma subunits of the heterotrimeric G proteins remain ti ghtly associated throughout the signaling cycle as the beta gamma dime r interacts with G alpha, receptors, and effecters, A coiled coil stru cture involving alpha-helical segments at the N termini of the beta an d gamma subunits contrib- utes to the dimerization interface and has b een implicated in effector signaling in yeast, Scanning mutagenesis of the coiled-coil region of the mammalian beta(1) subunit was performed to examine the effect of point mutations on py assembly and effector signaling in COS cell cotransfection assays, In addition to the E10K m utation described previously mutations A11E, L14E, and I18E in beta(1) were found to block beta gamma association, as evidenced by the failu re of the G beta mutants to undergo cytosolic translocation with cotra nsfected nonisoprenylated G gamma, Although none of 14 beta(1) point m utations prevented the beta gamma-dependent activation of the c-Jun N- terminal kinase (JNK) effector pathway, the D20K point mutation enhanc ed JNK but not phospholipase C-beta 2 activation, These findings impli cate the coiled-coil region of G beta in JNK signaling, provide furthe r evidence that the structural features of the beta gamma complex medi ating effector regulation may differ among effecters, and identify sin gle codons in the mammalian beta subunit where mutation might yield a phenotype of defective signal transduction.